In recent years, a magnetic disk apparatus has been widely used as a storage device for a computer. The magnetic disk apparatus rotates at high speed an aluminum or glass magnetic disk, on which a magnetic material is applied, by a motor and irradiates a magnetic field to a track on the magnetic disk by a magnetic head to record data (for example, see Japanese Laid-open Patent Publication No. 2008-77717). The magnetic disk apparatus may be one that records data with a track pitch of the magnetic disk fixed. The magnetic disk apparatus may also be an archive hard disk drive (HDD) that records data by narrowing down a track width to increase a recording density.
However, a conventional method performed by such an archive HDD that records data by narrowing down a track width of a magnetic disk tends to be influenced by a track edge due to variation in the track width.
The track width of the magnetic disk increases as a bit length increases because a magnetic field for recording the data is increased as the bit length increases. The track width of the magnetic disk decreases as the bit length decreases. Normally, data may have any bit length. Thus the track width varies depending on the bit length. Since the track width generally varies, a track edge is not smooth and changes.
FIG. 7 is an explanatory diagram for a problem in a conventional technology. Because the archive HDD records the data while narrowing down the track width, the track width does not have much margin. In the worst case, as the track width varies, previously recorded data may be overwritten by other data. In an example illustrated in FIG. 7, an area of a track A having a narrow track width is overwritten by an area of a track B having a wide track width.
Therefore, to increase a recording density by narrowing down a track pitch to record data as by the archive HDD, it is important to optimize the track width.